202 PALEONTOLOGY OF THE EUREKA DISTRICT. 



There are also a number of elongate, slender tubes, the relations of 

 which have not been determined. They are probably the young of one of 

 the smooth-tubed forms. 



Formation and localilities. Devonian limestone; Comb's Peak and Lone 

 Mountain, Eureka District, Nevada. 



Genus GOMPHOCERAS Sowerby. 



Gomphoceras suboviforme, n. sp. 

 Plate xvii, figs. 8, 8 a. 



Shell small, subglobose, attenuated towards the apex from the last 

 chamber. Transverse section subcircular. The point of greatest transverse 

 section of the grand chamber is a little anterior to the last septum. Tube 

 expanding regularly, with the sides nearly straight up to the chamber of 

 habitation, where it is somewhat inflated. Chamber of habitation rather 

 large, with the slightly convex ventral and lateral faces sloping gradually 

 to the apertural extremity, while the dorsal face, which is gently concave 

 above the zone of greatest transverse section, is at right angles to the plane 

 of the last septum. 



Air-chambers numerous, regular, not perceptibly increasing in depth 

 from where the tube is 10 mm in diameter to the chamber of habitation; 

 average depth nearly 2 mm , or ten chambers in a distance of 1 9 mm . Sutures 

 straight and horizontal. Siphuncle small, situated near the ventral margin; 

 diameter 2 mm , where the ventro-dorsal diameter of the tube is 17 mm ; its 

 structural elements are unknown, as the cast shows only the diameter. 



/ 



Internal mold of the tube apparently smooth. Length of chamber of habi- 

 tation (grand chamber), 18 mm ; greatest diameter, 24 mm ; length of tube, em- 

 bracing ten air-chambers, 19 mm ; anterior diameter of last chamber, 22 mm ; of 

 first apical chamber preserved in the specimen, 10 mm . 



This species is distinguished from G. oviforme Hall (Pal. N. Y., vol. v, 

 pt. 2, p. 344) of the Upper Helderberg Group of New York, by the more 

 attenuated and less ovate form, and the uniform and more shallow cham- 

 bers. It also resembles G.raphanus Hall (loc. cit., p. 347), of the Hamilton 



